Stamen

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Stamens of a Hippeastrum with white filaments and prominent anthers carrying pollen Amaryllis stamens aka.jpg
Stamens of a Hippeastrum with white filaments and prominent anthers carrying pollen

The stamen (plural stamina or stamens) is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium. [1]

Contents

Morphology and terminology

A stamen typically consists of a stalk called the filament and an anther which contains microsporangia . Most commonly anthers are two-lobed and are attached to the filament either at the base or in the middle area of the anther. The sterile tissue between the lobes is called the connective, an extension of the filament containing conducting strands. It can be seen as an extension on the dorsal side of the anther. A pollen grain develops from a microspore in the microsporangium and contains the male gametophyte.

The stamens in a flower are collectively called the androecium. The androecium can consist of as few as one-half stamen (i.e. a single locule) as in Canna species or as many as 3,482 stamens which have been counted in the saguaro (Carnegiea gigantea). [2] The androecium in various species of plants forms a great variety of patterns, some of them highly complex. [3] [4] [5] [6] It generally surrounds the gynoecium and is surrounded by the perianth. A few members of the family Triuridaceae, particularly Lacandonia schismatica , are exceptional in that their gynoecia surround their androecia.

Hippeastrum flowers showing stamens above the style (with its terminal stigma) Hippeastrum-1.jpg
Hippeastrum flowers showing stamens above the style (with its terminal stigma)
Closeup of stamens and stigma of Lilium 'Stargazer' Closeup of Lilium 'Stargazer' (the 'Stargazer lily').jpg
Closeup of stamens and stigma of Lilium 'Stargazer'

Etymology

Variation in morphology

Stamens, with distal anther attached to the filament stalk, in context of floral anatomy Mature flower diagram.svg
Stamens, with distal anther attached to the filament stalk, in context of floral anatomy

Depending on the species of plant, some or all of the stamens in a flower may be attached to the petals or to the floral axis. They also may be free-standing or fused to one another in many different ways, including fusion of some but not all stamens. The filaments may be fused and the anthers free, or the filaments free and the anthers fused. Rather than there being two locules, one locule of a stamen may fail to develop, or alternatively the two locules may merge late in development to give a single locule. [12] Extreme cases of stamen fusion occur in some species of Cyclanthera in the family Cucurbitaceae and in section Cyclanthera of genus Phyllanthus (family Euphorbiaceae) where the stamens form a ring around the gynoecium, with a single locule. [13]

Cross section of a Lilium stamen, with four locules surrounded by the tapetum Antera Lilium.jpg
Cross section of a Lilium stamen, with four locules surrounded by the tapetum

Pollen production

A typical anther contains four microsporangia. The microsporangia form sacs or pockets (locules) in the anther (anther sacs or pollen sacs). The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called the tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis. Each microspore then divides mitotically to form an immature microgametophyte called a pollen grain.

The pollen is eventually released when the anther forms openings (dehisces). These may consist of longitudinal slits, pores, as in the heath family (Ericaceae), or by valves, as in the barberry family (Berberidaceae). In some plants, notably members of Orchidaceae and Asclepiadoideae, the pollen remains in masses called pollinia, which are adapted to attach to particular pollinating agents such as birds or insects. More commonly, mature pollen grains separate and are dispensed by wind or water, pollinating insects, birds or other pollination vectors.

Pollen of angiosperms must be transported to the stigma, the receptive surface of the carpel , of a compatible flower, for successful pollination to occur. After arriving, the pollen grain (an immature microgametophyte) typically completes its development. It may grow a pollen tube and undergoing mitosis to produce two sperm nuclei.

Sexual reproduction in plants

Stamen with pollinia and its anther cap. Phalaenopsis orchid. Phalaenopsis orchid-Stipe.jpg
Stamen with pollinia and its anther cap. Phalaenopsis orchid.

In the typical flower (that is, in the majority of flowering plant species) each flower has both carpels and stamens. In some species, however, the flowers are unisexual with only carpels or stamens. ( monoecious = both types of flowers found on the same plant; dioecious = the two types of flower found only on different plants). A flower with only stamens is called androecious. A flower with only carpels is called gynoecious.

A flower having only functional stamens and lacking functional carpels is called a staminate flower, or (inaccurately) male. [14] A plant with only functional carpels is called pistillate, or (inaccurately) female. [14]

An abortive or rudimentary stamen is called a staminodium or staminode , such as in Scrophularia nodosa .

The carpels and stamens of orchids are fused into a column. The top part of the column is formed by the anther, which is covered by an anther cap.

Descriptive terms

Scanning electron microscope image of Pentas lanceolata anthers, with pollen grains on surface Penta anther.jpg
Scanning electron microscope image of Pentas lanceolata anthers, with pollen grains on surface
Lily stamens with prominent red anthers and white filaments Lily stamens.jpg
Lily stamens with prominent red anthers and white filaments
Begonia grandis stamens Qiu Hai Tang 20191106164316 07.jpg
Begonia grandis stamens
Sterculia foetida stamens Xiang Pin Po Sterculia foetida 20210409164154 01.jpg
Sterculia foetida stamens
Stamen of a Grevillea robusta Yin Hua Grevillea robusta 20210411152016 14.jpg
Stamen of a Grevillea robusta
Stamen

Stamens can also be adnate (fused or joined from more than one whorl):

They can have different lengths from each other:

or respective to the rest of the flower (perianth):

They may be arranged in one of two different patterns:

They may be arranged, with respect to the petals:

Connective

Where the connective is very small, or imperceptible, the anther lobes are close together, and the connective is referred to as discrete, e.g. Euphorbia pp., Adhatoda zeylanica . Where the connective separates the anther lobes, it is called divaricate, e.g. Tilia , Justicia gendarussa . The connective may also be a long and stalk-like, crosswise on the filament, this is a distractile connective, e.g. Salvia . The connective may also bear appendages, and is called appendiculate, e.g. Nerium odorum and some other species of Apocynaceae. In Nerium, the appendages are united as a staminal corona.

Filament

A column formed from the fusion of multiple filaments is known as an androphore. Stamens can be connate (fused or joined in the same whorl) as follows:

Anther

Anther shapes are variously described by terms such as linear, rounded, sagittate, sinuous, or reniform.

The anther can be attached to the filament's connective in two ways: [16]

Related Research Articles

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Petal Part of most types of flower

Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called corolla. Petals are usually accompanied by another set of modified leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth. When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly colored tepals. Since they include Liliales, an alternative name is lilioid monocots.

Column (botany)

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Gynoecium The female organs of a flower

Gynoecium is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of pistils and is typically surrounded by the pollen-producing reproductive organs, the stamens, collectively called the androecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which then produces egg cells.

Sabiaceae

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Calyceraceae Family of flowering plants

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Whorl (botany)

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